Electrodynamics and energy characteristics of aurora at high resolution by optical methods

Technological advances leading to improved sensitivity of optical detectors have revealed that aurora contains a richness of dynamic and thin filamentary structures, but the source of the structured emissions is not fully understood. In addition, high resolution radar data have indicated that thin auroral arcs can be correlated with highly varying and large electric fields, but the detailed picture of the electrodynamics of auroral filaments is yet incomplete. The ASK instrument is a state-of-the-art ground-based instrument designed to investigate these smallest auroral features at very high spatial and temporal resolution, by using three EMCCDs in parallel for three different narrow spectral regions. ASK is specifically designed to utilize a new optical techique to determine the ionospheric electric fields. By imaging the long-lived O+ line at 732~nm, the plasma flow in the region can be traced, and since the plasma motion is controlled by the electric field, the field strength and direction can be estimated at unprecedented resolution. The method is a powerful tool to investigate the detailed electrodynamics and current systems around the thin auroral filaments. The two other ASK cameras provide information on the precipitation by imaging prompt emissions, and the emission brightness ratio of the two emissions, together with ion chemistry modeling, is used to give information on the energy and energy flux of the precipitating electrons. In this paper, we discuss these measuring techniques, and give a few examples of how they are used to reveal the nature and source of fine scale structuring in the auror

A scientific career launched at the start of the space age: Michael Rycroft at 80

The scientific career of Michael Rycroft (born in 1938) spans the space age, during which significant changes have occurred in how scientists work, experiment, and interact. Here, as part of his 80th birthday celebrations, we review his career to date in terms of the social and structural changes in collaborative international science. His contributions to research, teaching, and management across solar–terrestrial and ionospheric physics as well as atmospheric and space science are also discussed

ASK keograms and videos for study on variations in energy, flux and brightness of pulsating aurora measured at high time resolution

Dataset for &quot;Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution&quot;, Dahlgren, H., et al., Ann. Geophys., 2017. Dataset consists of 2 videos from the Auroral Structure and Kinetics (ASK) instrument, operated by the University of Southampton, UK and Royal Institute of Technology, Stockholm. Also included are &quot;keograms&quot; from 22 October 2006 and 19 January 2007. See the included README.txt file for more information.</span

High-resolution optical observations of neutral heating associated with the electrodynamics of an auroral arc

We present results that indicate the existence of two distinct neutral heating processes associated with a discrete auroral arc over Svalbard. Within the order of seconds, the thermospheric temperature profile displays a significant response to the arc on spatial scales smaller than 10 km. It is suggested that both heating signatures are associated with the electrodynamic system responsible for the formation of the arc. Pedersen currents produce a temperature increase of approximately 100 K, observed at altitudes between 80 and 160 kilometres, directly adjacent to the arc structure and on its poleward edge only. In contrast, field‐aligned currents produce a variable temperature increase, of approximately 50 K, which is observed within the arc itself and constrained to a narrow altitude range between 90 and 110 km. By utilizing a range of observations and new analysis methods we are able to measure the atmospheric neutral temperature profile, over auroral altitudes, at unprecedented temporal and spatial scales. The High Throughput Imaging Echelle Spectrograph records high‐resolution emission spectra of the aurora, which are then fitted with synthetic N2 spectra, generated with modeled N2 volume emission rate profiles and a library of trial temperature profiles. The N2 volume emission rate profiles are retrieved from the Southampton ionospheric model using precipitating particle energies and fluxes obtained from Auroral Structure and Kinetics and the EISCAT Svalbard Radar. The application of this technique allows us to produce a time series of neutral temperature profiles and measure the localized heating of the neutral atmosphere resulting from the electrodynamics of the arc

Dataset for High resolution optical observations of neutral heating associated with the electrodynamics of an auroral arc

This dataset supports the publication: Price, D. J. et al (2020). High resolution optical observations of neutral heating associated with the electrodynamics of an auroral arc. Journal of Geophysical Research - Space Physics.</span

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

High-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall

Dataset for journal paper &quot;Fine-scale electric fields and Joule heating from observations of the Aurora&quot;

To be published in the Journal of Geophysical Research: Space Physics In article &quot;Fine-scale electric fields and Joule heating from observations of the Aurora&quot; we have combined Southampton led Auroral Structure and Kinetics (ASK) instrument with careful modeling to obtain high resolution electric fields associated with small-scale auroral features. We have combined our measurements with Scanning Doppler Imager (SCANDI) to obtain Joule heating estimates and compare them with more commonly used averaged SuperDARN measurements. Our results show that observation of small-scale Joule heating gives much higher values than the one obtained from averaged radar data. Dataset used in the article is available at: https://doi.org/10.5258/SOTON/D2501. Dataset consist of 3 files: ASK.zip, SuperDARN.zip, SCANDI.zip. ASK.zip has 3 folders: ASK1, ASK2 and ASK3. Each folder contains the files from separate ASK camera as explained in the paper. Data are stored in .txt files each labeled with the timestep. Each .txt file contains 256x256 matrix with pixel values obtained during given timestep. SCANDI.zip contains a .xlsx file with all the measurements from a single measurement sweep needed to obtain neutral wind velocity data presented in the paper. SuperDARN.zip contains the typical SuperDARN toolkit .grdmap and .map data types.</span

Fine-scale electric fields and Joule heating from observations of the Aurora

Optical measurements from three selected wavelengths have been combined with modelling of emissions from an auroral event to estimate the magnitude and direction of small-scale electric fields on either side of an auroral arc. The temporal resolution of the estimates is 0.1 seconds, which is much higher resolution than measurements from SuperDARN in the same region, with which we compare our estimates. Additionally, we have used the SCANDI instrument to measure the neutral wind during the event in order to calculate the height integrated Joule heating. Joule heating obtained from the small scale electric fields gives larger values (17 ± 11 and 6 ± 9 mWm −2 on average on each side of the arc) than the Joule heating obtained from more conventionally used SuperDARN data (5 mWm −2 ). This result is significant, because Joule heating will cause changes in the thermosphere from thermal expansion and thermal conductivity, and may also affect the acceleration of the neutral wind. Our result indicates that high spatial and temporal resolution electric fields may play an important role in the dynamics of the magnetosphere-ionosphere-thermosphere system